Abstract

A major challenge in volcanology is determining the factors that control the frequency
and magnitude of eruptions at hazardous caldera volcanoes. Understanding the critical
sequence of events that may lead to future eruptions is vital for volcanic monitoring and risk
assessment. Here we use magma chemistry and mineral diffusion modeling to interpret the
magmatic processes and time scales involved in the youngest three eruptions (2.15–1.7 ka)
from Taupo volcano (New Zealand), which peaked with the voluminous A.D. 232 eruption.
Of the rhyolites erupted since ca. 12 ka, the <2.15 ka magmas have the lowest whole-rock
SiO2 content and reversely zoned crystals, yet with high-SiO2 melt inclusions. Mineral zonations
and compositional shifts reflect a 30–40 °C temperature increase over the immediately
preceding (>2.75 ka) rhyolites that were tapped from the same magma reservoir. Orthopyroxene
Fe-Mg diffusion time scales indicate that the onset of rapid heating and priming of
the host silicic mush occurred <120 yr prior to the <2.15 ka eruptions, with subsequent melt
accumulation occurring in only decades. Elevated mafic magma supply to the silicic mush
pile, rapid melt accumulation, and high differential tectonic stress built up and culminated
in the ∼105 km3 A.D. 232 eruption, one of the largest and most violent Holocene eruptions
globally. These youngest eruptions demonstrate how Taupo's magmatic system can rapidly
change behavior to generate large eruptible melt bodies on time scales of direct relevance to
humans and monitoring initiatives.